The present invention relates generally to a hologram ate and its fabrication process, and more specifically to a hologram plate designed to replicate a hologram array comprising collective element holograms such as hologram color filters, and its fabrication process.
The present invention is also concerned with a multifaceted hologram plate and its fabrication process.
Further, the present invention is directed to the construction of a protective film for a hologram plate.
In JP-A 06-222361, etc., the applicant has already come up with a hologram-harnessing color filter for the purpose of greatly increasing the efficiency of utilization of liquid crystal display backlights, etc. This hologram color filter is basically made up of an array of a transmission type of collective element holograms capable of diffracting parallel light incident thereon at a specific wavelength and a specific angle of oblique incidence in such a way that it is converged on a specific focal distance position.
To use such a hologram array as a hologram plate to replicate another hologram array having similar properties by a hologram replication process, for instance, a first hologram plate is fabricated in the form of a computer-generated hologram (CGH). Then, the first hologram plate is replicated by the hologram replication process to fabricate a hologram plate, from which the final product is fabricated by a similar hologram replication process.
To replicate such a transmission type of collective element hologram array as mentioned above, the applicant has filed a patent application (JP-A 09-90860) to come up with a process wherein when replicas of the first plate and hologram plate are fabricated, the distance between the hologram plate and a hologram photosensitive material is fixed to substantially double the focal length of each element hologram to make a hologram replica having similar properties to those of the hologram plate. This process is now explained with reference to FIG. 12.
FIG. 12 is illustrative of how to fabricate a hologram array 5 providing a hologram color filter from a CGH array plate 7 in one single replication operation. A plate for a hologram array 5 providing a hologram color filter is constructed in the form of a CGH array 7. The distance from the relief surface of the CGH array plate 7 to a photosensitive layer 13 is fixed to 2f that is double the focal length f of each CGH 5xe2x80x3 so that a hologram photosensitive material 8 is spaced away from the CGH array plate 7. Laser light 9 having a specific wavelength is entered into the CGH array plate 7 at a specific angle of incidence, so that diffracted light 10, converged by the diffraction action of each CGH 5xe2x80x3 from convergent light to divergent light, and straightforwardly traveling transmitted light 11 interfere in the photosensitive layer 13 of the hologram photosensitive material 8.
Here let D represent the diameter of a recording area of each element hologram 5xe2x80x3 of the CGH array plate 7. Then, the diffracted light 10, once converged on a position P located at a distance f from the relief surface of each CGH 5xe2x80x3, is converged on a 2f position into a divergent light beam having the same diameter D. Accordingly, if the divergent light and the straitghtforwardly traveling transmitted light 11 interfere in the photosensitive layer 13 located at this position, the diameter of the hologram interference fringe recording area becomes equal to D, and the pitch between adjacent replicated element holograms becomes equal to that between adjacent element holograms 5xe2x80x3 of the CGH array plate 7 as well. In addition, when light traveling in the opposite direction to the transmitted light for hologram array replication is entered in the thus replicated hologram array from the glass substrate 12 side, the diffracted light is converged on a position P at a length f from the photosensitive layer 13 with hologram interference fringes recorded therein, and so has the same diameter as the focal length of each element hologram 5xe2x80x3 of the CGH array plate 7. In other words, a hologram array completely identical with the CGH array plate 7 is obtained.
The hologram array replicated from the CGH array plate 7 in such an arrangement as shown in FIG. 12 is then used as a hologram plate to obtain the end product. FIG. 13 is illustrative of one arrangement of how to carry out such second replication operation. In FIG. 13, H1 stands for an intermediate hologram array obtained by replication in the arrangement of FIG. 12. This intermediate hologram array H1 is again used as a hologram plate for replication purposes. In this case, the hologram photosensitive material 8 is located on the side of the plate 7 for the replication of the intermediate hologram array H1, and reconstructing illumination laser light 9xe2x80x2 is entered in the intermediate hologram array H1 from the opposite direction to the transmitted light 11 for the replication of the intermediate hologram array H1, and the distance from the diffraction surface of the intermediate hologram array H1 to the photosensitive layer 13 of the hologram photosensitive material 8 is fixed to 2f that is double the focal length f of each element hologram. When the reconstructing illumination laser light 9 is entered in the intermediate hologram array H1 in such an arrangement, light 10xe2x80x2 diffracted by each element hologram of the intermediate hologram array H1 travels in the opposite direction to the diffracted light 10 of FIG. 12 and, once converged, is converted at the 2f position to a divergent light beam having the same diameter D. Accordingly, diffracted light 10xe2x80x2 and straightforwardly traveling transmitted light 11xe2x80x2 interfere in the photosensitive layer 13 located at this position as in the case of FIG. 12, so that an array of element holograms having the same focal length f is replicated and recorded at a pitch d in the area having the same diameter D.
The feature of this process is that a hologram similar in properties to the hologram plate can be fabricated even when the hologram plate is in no perfect contact with the replica. In what follows, the hologram replication process in such an arrangement will be called a double-focus replication process.
Incidentally, hologram photosensitive materials such as photopolymers are generally poor in marring resistance whether in an unrecorded state or in a state subjected to post-recording treatments. When replication is carried out with a hologram plate in close contact with a hologram photosensitive material, it is likely that the hologram on the hologram plate side is immediately damaged and some of the photosensitive material on the replication side peels off, depositing onto the hologram on the hologram plate side. Such depositions are hardly removable.
When a hologram has such a focal length as mentioned above, there is a variation in the focal length of replicas due to a contact gap at the time of replication, and a variation in gap thickness leads to a variation in the focal length of replicas.
It is desired that the zero-order light and first-order light diffracted by the hologram plate have substantially the same intensity at the position of the hologram photosensitive material. To this end, it is required to place the refractive index modulation under severe control. However, this control is difficult on practical levels.
The hologram (intermediate hologram array HI) used for the replication of the end products is herein called the hologram plate. When a hologram plate having only one hologram (hologram color filter) equivalent to one segment is used for the replication of such a color filter as mentioned above, however, replication efficiency becomes worse.
To avoid this, a process has been proposed in the art, which process makes use of a hologram plate obtained by translating a CGH plate 7 with respect to one large hologram photosensitive material 8 for a plurality of replication cycles wherein, for instance, four or eight holograms are exposed to light to form four or eight juxtaposed holograms in the hologram photosensitive material, so that four or eight holograms can be simultaneously replicated in one replication operation. Such a hologram plate with a plurality of juxtaposed holograms is called a multifaceted hologram plate.
As shown in FIG. 13, for instance, the multifaceted hologram plate is prepared in plural replication operations, using a CGH plate with respect to one large hologram photosensitive material. However, when at least one of plural exposure operations (replication operations from the CGH plate) is improper, the resultant multifaceted hologram plate cannot be used or fails to provide a hologram plate having good replication efficiency.
In view of such prior art states as mentioned above, the first object of the present invention is to provide a hologram plate used with the double-focus replication process, which is integrated with a spacer to impart marring resistance thereto, and is integrated with a light absorbing layer to allow zero-order light and first-order light to have substantially the same intensity, and its fabrication process.
The second object of the present invention is to provide a multifaceted hologram plate which can have hologram segments of improved properties, can be used for efficient replication, and has improved durability, and its fabrication process.
The third object of the present invention is to provide an easily releasable protective film for a hologram plate, which prevents surface marring, wearing and contamination at the time of contact replication or removal of foreign matters.
According to the present invention, the aforesaid first objet is achieved by the provision of a hologram plate comprising an array of a transmission type of collective element holograms that diffract parallel light incident thereon at a specific wavelength and a specific angle of incidence in such a way that the parallel light is converged on a specific focal length position, characterized by comprising a multilayer structure made up of a first transparent substrate, a hologram layer, an adhesive layer and a second transparent layer, said second transparent substrate defining a surface into contact with a hologram photosensitive material when hologram replication is carried out.
Preferably in this case, the second transparent substrate should have a thickness that is substantially twice the focal length of each collective element hologram, inclusive of the thickness of the adhesive layer.
Preferably, a water-soluble protective layer should be interleaved between the hologram layer and the adhesive layer.
Preferably in the case mentioned just above, the second transparent substrate should have a thickness that is substantially twice the focal length of each collective element hologram, inclusive of the thicknesses of the adhesive layer and water-soluble protective layer.
The diffraction efficiency of the hologram layer may be preset in such a way as to allow the zero-order light and first-order light diffracted by the hologram layer to have substantially the same intensity.
An absorbing layer may be interleaved at any desired position between the hologram layer and the second transparent layer, and a light absorbing material is dispersed throughout the absorbing layer in such a way as to allow the zero-order light and first-order light diffracted by the hologram layer to have substantially the same intensity.
An absorbing layer may be located on the surface of the second transparent substrate, and a light absorbing material is dispersed throughout the absorbing layer in such a way as to allow the zero-order light and first-order light diffracted by the hologram layer to have substantially the same intensity.
According to the present invention, there is also provided a process for fabricating the hologram plate for the purpose of achieving the aforesaid first object of the present invention, characterized in that:
said adhesive layer comprises an ultraviolet curing adhesive agent,
said multilayer structure, obtained by forming said hologram layer on said first transparent substrate and then superposing said second transparent substrate on said hologram layer with an uncured ultraviolet curing adhesive agent interleaved therebetween, is spun to spin an extra portion of said adhesive agent out of the periphery thereof, thereby making said adhesive layer uniform, while the rpm of said multilayer structure is controlled to obtain a desired thickness, and
said multilayer structure is irradiated with ultraviolet radiation through said first transparent substrate or said second transparent substrate to cure said adhesive agent.
Preferably in this case, the hologram layer is exposed to p-polarized light. P-polarized light is more reduced in interface reflection than s-polarized light, so that unnecessary interference fringes can be reduced during exposure and xcex94n (refractive index modulation) can be controlled to a reduced value as well.
However, when the diffraction efficiency of the CGH plate is too low as an example, the use of s-polarized light is preferable because xcex94n can be increased with an increased diffraction efficiency.
In the present invention for the purpose of achieving the aforesaid first object, the hologram plate comprises a multilayer structure made up of a first transparent substrate, a hologram layer, an adhesive layer and a second transparent layer and the second transparent substrate defines a surface in contact with a hologram photosensitive material during hologram replication, so that the second transparent substrate can function as a protective layer to make the hologram plate resistant to marring. In addition, the second transparent substrate can be used as a spacer for a double-focus replication process wherein the distance between the hologram plate and the hologram photosensitive material is set at substantially double the focal length of each collective element hologram, so that replicas can be fabricated with constant focal lengths.
An absorbing layer is located between the hologram layer and the adhesive layer or at other position to allow the zero-order light and first-order light diffracted by the hologram layer to have substantially the same intensity, so that hologram replicas of high diffraction efficiency can be obtained.
The present invention has been described with reference to the double-focus fabrication process. It is noted, however, that it is actually important and desirous to keep the distance between the hologram plate and the photosensitive material constant in consideration of the total thickness of all members inclusive of the adhesive layer, protective layer and index matching liquid.
When the first replication is carried out in the contact mode and the second is carried out by the double-focus replication process, it is desired that the distance coincide with the value obtained by the subtraction of the first replication gap from the value double the focal length.
The aforesaid second object of the present invention is achieved by the provision of a hologram plate comprising a plurality of juxtaposed unit hologram segments, characterized in that:
one common transparent thin sheet is provided over the surfaces of said plurality of juxtaposed unit hologram segments with an adhesive agent interleaved therebetween.
Preferably in this case, each unit hologram segment should comprise a transparent substrate, a photosensitive material layer formed thereon while a hologram is recorded therein, and a protective layer formed on said photosensitive material layer.
It is here preferable that a transparent thin sheet should be bonded onto said protective layer for each unit hologram segment.
It is also preferable that said plurality of unit hologram segments should be hologram segments replicated from the same hologram plate.
Each unit hologram segment, for instance, may be a hologram color filter.
Regarding the aforesaid second object of the present invention, there is provided a process for fabricating a hologram plate comprising a plurality of juxtaposed unit hologram segments and one common transparent sheet provided over the surfaces of said unit hologram segments with an adhesive agent interleaved therebetween, characterized by comprising steps of:
preparing a plurality of unit hologram segments,
adsorbing a transparent thin sheet onto the surface of a reference plate and laminating said plurality of unit hologram segments, in juxtaposed relation to each other, on said transparent thin sheet with an adhesive agent interleaved therebetween,
bonding a base plate onto the back side of said plurality of juxtaposed unit hologram segments with an adhesive agent interleaved therebetween, and
desorbing said transparent thin sheet from said reference plate to release said transparent thin sheet from said reference plate.
Preferably in this process, at the step of preparing a plurality of unit hologram segments, said plurality of unit hologram segments are replicated from the same hologram plate.
According to the present invention for achieving the aforesaid second object, all the unit holograms can be precisely replicated because the unit hologram segments are kept flush with one another by one common thin sheet glass provided over the plurality of juxtaposed unit hologram segments. When the hologram photosensitive material is brought into close contact with the multifaceted hologram plate with an index matching liquid applied therebetween for the purpose of hologram replication, it is extremely unlikely that an optical adhesive agent between adjacent unit hologram segments will be dissolved in the index matching liquid. If a glass sheet is used as the transparent thin sheet, improved durability is then obtained. Fabricated by the lamination of only unit hologram segments put in good alignment with good properties, the multifaceted hologram plate according to the present invention for achieving the aforesaid second object have all unit hologram segments of good quality and uniform properties, and so can be used for hologram replication with high efficiency.
According to the present invention for achieving the aforesaid third object, there is provided a hologram plate comprising a hologram layer with interference fringes formed thereon, a first layer capable of being removed with water or a solvent, which is provided on the surface of said hologram layer or a transparent layer formed thereon, and a second layer of a curing resin capable of being cured by light or heat, which is formed on said first layer.
In this hologram plate, the hologram layer may be either an amplitude type hologram layer with a metal film patterned thereon or a hologram layer comprising a hologram photosensitive material layer with interference fringes recorded therein.
The first layer may have the property of absorbing light.
This hologram plate may be applied to either a transmission type hologram or a reflection type hologram.
Thus, the hologram plate for achieving the aforesaid third object of the present invention comprises a hologram layer with interference fringes formed thereon, a first layer capable of being removed with water or a solvent, which is provided on the surface of said hologram layer or a transparent layer formed thereon, and a second layer of a curing resin capable of being cured by light or heat, which is formed on said first layer. The second layer functions as a protective layer for the hologram layer 202, thereby preventing the marring, wearing and contamination of the hologram layer, which may otherwise occur at steps of coating an index matching liquid, carrying out contact replication, removing the index matching liquid, removing foreign matters, and so on. As many holograms are replicated, the second layer, too, is subjected to marring, wearing and contamination. In this case or, for instance, when one fails to form the first layer or the second layer, the hologram plate is washed with water or boiled in boiling water, so that the protective layer can be easily removed. Then, if fresh first and second layers are provided on the hologram layer, the hologram plate can be regenerated.
Still other objects and advantages of the invention will in part be obvious and will in part be apparent from the specification.
The invention accordingly comprises the features of construction, combinations of elements, and arrangement of parts which will be exemplified in the construction hereinafter set forth, and the scope of the invention will be indicated in the claims.